First-ever Hyperspectral Images of Earth’s Auroras:
New camera provides tantalizing clues of new atmospheric phenomenon
The NORUSCA II camera was tested at the Kjell Henriksen Observatory (KHO) by UNIS staff together with
colleagues from Russia, Ukraine and Canada. (Photo: Njål Gulbrandsen/UNIS).
November 29, 2012
The spectacular night-sky displays known as the Northern Lights just got more spectacular! The staff at the Kjell Henriksen
Observatory, together with colleagues from Russia, Ukraine and Canada, has for the first time imaged Earth’s auroras with
unprecedented clarity—simultaneously capturing multiple spectral bands of light at once. The images from the new camera also
revealed a previously unknown atmospheric phenomenon—a natural emission of light known as airglow interacting with the aurora.
Hoping to expand our understanding of auroras and other fleeting atmospheric events, a team of space-weather researchers designed
and built NORUSCA II, a new camera with unprecedented capabilities that can simultaneously image multiple spectral bands,
in essence different wavelengths or colors, of light.
The camera was tested at the
Kjell Henriksen Observatory (KHO)
in Svalbard, where it produced the first-ever hyperspectral images of auroras—commonly referred to as
“the Northern (or Southern) Lights”—and may already have revealed a previously unknown atmospheric phenomenon.
Details on the camera and the results from its first images were published today in the Optical Society’s open-access
journal Optics Express.
Auroras, nature’s celestial fireworks, are created when charged particles from the Sun penetrate Earth's magnetic field.
These shimmering displays in the night sky reveal important information about the Earth-Sun system and the way our planet
responds to powerful solar storms.
Current-generation cameras, however, are simply light buckets—meaning they collect all the light together into one image—and
lack the ability to separately capture and analyze multiple slivers of the visible spectrum. That means if researchers want to
study auroras by looking at specific bands or a small portion of the spectrum they would have to use a series of filters to block
out the unwanted wavelengths.
The new NORUSCA II hyperspectral camera achieves the same result without any moving parts, using its advanced optics to switch
among all of its 41 separate optical bands in a matter of microseconds, orders of magnitude faster than an ordinary camera.
This opens up new possibilities for discovery by combining specific bands of the same ethereal phenomenon into one image,
revealing previously hidden details.
UNIS professor Fred Sigernes.
- A standard filter wheel camera that typically uses six interference filters will not be able spin the wheel fast enough compared
to the NORUSCA II camera, says
professor Fred Sigernes
of the University Centre in Svalbard (UNIS).
- This makes the new hyperspectral capability particularly useful for spectroscopy, because it can detect specific atmospheric
constituents by their unique fingerprint, or wavelengths, in the light they emit, he explains.
These spectral signatures can then reveal subtle changes in atmospheric behavior, such as the ionization of gases during auroras.
This form of multispectral imaging also will enable scientists to better classify auroras from background sky emissions and study
the way they cluster in the atmosphere.
A New Phenomenon
On Jan. 24, 2012, during the inaugural research campaign of NORUSCA II, a major solar flare jettisoned a burst
of high-energy particles known as a Coronal Mass Ejection (CME). The CME eventually slammed into Earth’s magnetic field,
producing magnificent auroras and a chance to fully test the new camera.
The researchers were able to image the aurora in unprecedented clarity through a layer of low altitude clouds,
which would have thwarted earlier-generation instruments.
The camera also revealed something unexpected -- a very faint wave pattern of unknown origin in the lower atmosphere.
The wave pattern resembles “airglow” – the natural emission of light by Earth’s atmosphere. Airglow can be produced by a
variety of known sources, including cosmic rays and chemical reactions. Its concurrent appearance with the aurora suggests
that it may also be caused by a previously unrecognized source.
- After the January CME, we think we saw an auroral-generated wave interaction with airglow, said Sigernes.
This would be an entirely new phenomenon and if confirmed, would be the first time airglow has been associated with auroras,
- Our new all-sky camera opens up new frontiers of discovery and will help in the detection of auroras and the understanding
of how our Sun impacts the atmosphere here on Earth. Additional development and commissioning will also hopefully verify our
intriguing first results,” concludes Sigernes.
Part A – The aurora as seen as a color composite image from the NORUSCA II camera.
Three bands were combined to make the image. Each band was assigned a different color -- red, green,
and blue – to enhance the features of the aurora for analysis.
Part B - The red arrow points to the unidentified low-intensity wave pattern, which the researchers suspect
is an auroral-generated wave interaction with airglow. For contrast, the blue arrow points to the faint emission
of the Milky Way. (Credit: Optics Express).
Fred Sigernes, Yuriy Ivanov, Sergey Chernouss, Trond Trondsen, Alexey Roldugin, Yury Fedorenko, Boris Kozelov, Andrey Kirillov,
Ilia Kornilov, Vladimir Safargaleev, Silje Holmen, Margit Dyrland, Dag Lorentzen and Lisa Baddeley:
“Hyper-Spectral All-Sky Imaging of Auroras,” Optics Express, Vol. 20, Issue 25, pp. 27650-27660 (2012).